Single-tooth prosthodontic restorations present the unique requirement that they must be supported non-rotationally on the underlying abutment. When a prepared natural tooth is the underlying abutment this requirement is met in the normal course of preparing the abutment with a non-circular cross-section. Likewise, when the underlying abutment is a post fitted into a root canal this requirement is met by preparing the post with a noncircular cross-section. But, when the underlying abutment is itself supported on a dental implant fixture these options are not available to the prosthodontist. One technique that is available is to anchor the restoration to one or both of the adjacent natural teeth; however this technique requires that the adjacent tooth or teeth be prepared, as by grinding away some part of existing healthy enamel and dentin to accept a supporting fixture, which is undesirable.
A dental implant fixture is implanted into the bone of a patient's jaw and supports a socket which is accessible through the overlying gum tissue for receiving and supporting one or more attachments or components which in turn are useful to fabricate and to support the prosthodontic restoration. Dental implant fixtures can use a variety of implanting modalities; i.e.: blade, bone screw or smooth post, as examples. The present invention is not concerned with the implant modality that is used. The invention is concerned with the fact that the sockets of many of the most successful dental implant fixtures presently in use are cylindrical in shape; if the socket is internally threaded no other internal shape is possible. Such a socket, by itself, cannot provide non-rotational fixing of a single-tooth prosthodontic restoration to a dental implant fixture. To overcome that deficiency some of the dental implant fixtures that are now available include anti-rotation mean to restrain components attached to the fixture against rotation relative to the implant fixture around the longitudinal axis through the socket. A common example is a polygonal (e.g.: hexagonal) male projection or female indentation located on the gingival surface of the implant concentric with the opening into the socket.